Alkanes Nomenclature The name of every organic molecule

Alkanes - Nomenclature The name of every organic molecule has 3 parts: 1. The parent (root) name indicates the # of carbons in the longest continuous chain 2. The suffix indicates what functional group is present. 3. The prefix tells us the identity, location, and number of substituents attached to the carbon chain.

Alkanes - Nomenclature Parent – Longest contiguous carbon chain

Alkanes - Nomenclature Suffix – Our first functional group is alkane, so the suffix is –ane For later functional groups we will drop the –ane root suffix for others Alkane chain # Carbons Name CH 4 1 methane CH 3 2 ethane CH 3 CH 2 CH 3 3 propane CH 3 CH 2 CH 3 4 butane CH 3 CH 2 CH 2 CH 3 5 pentane CH 3 CH 2 CH 2 CH 3 6 hexane CH 3 CH 2 CH 2 CH 2 CH 3 7 heptane CH 3 CH 2 CH 2 CH 2 CH 3 8 octane CH 3 CH 2 CH 2 CH 3 9 nonane CH 3 CH 2 CH 2 CH 3 10 decane CH 3 CH 2 CH 2 CH 2 CH 3 11 undecane CH 3 CH 2 CH 2 CH 2 CH 3 12 dodecane

Alkanes - Nomenclature Prefix – Our substituents will be branches in the alkane structure A branch is another alkane minus one hydrogen – an alkyl group Example – if CH 3 - is a branch on a longer chain: CH 3 - is CH 4 minus 1 hydrogen Since it is a side chain it will replace the –ane suffix with –yl CH 3 - is a methyl group We can also abbreviate this group as Me-

Alkanes - Nomenclature Prefixes Alkyl group CH 3 - Structure CH 3 - IUPAC name Abbreviation methyl Me- CH 3 CH 2 - ethyl Et- CH 3 CH 2 - n-propyl n-Pr CH 3 CHCH 3 isopropyl or i-propyl i-Pr CH 3 CH 2 CH 2 - n-butyl n-Bu CH 3 CH 2 CHCH 3 sec-butyl s-Bu (CH 3)2 CHCH 2 - isobutyl or i-butyl i-Bu (CH 3)3 C- tert-butyl or t-butyl t-Bu C 6 H 5 - phenyl Ph

Alkanes - Nomenclature 1. Find the parent carbon chain and add the suffix. Note that it does not matter if the chain is straight or it bends.

Alkanes - Nomenclature Also note that if there are two chains of equal length, pick the chain with more substituents. In the following example, two different chains in the same alkane have seven C atoms. We circle the longest continuous chain as shown in the diagram on the left, since this results in the greater number of substituents.

Alkanes - Nomenclature 2. Number the atoms in the carbon chain to give the first substituent the lowest number.

Alkanes - Nomenclature If the first substituent is the same distance from both ends, number the chain to give the second substituent the lower number.

Alkanes - Nomenclature When numbering a carbon chain results in the same numbers from either end of the chain, assign the lower number alphabetically to the first substituent.

Alkanes - Nomenclature 3. Name and number the substituents. • • Name the substituents as alkyl groups. Every carbon belongs to either the longest chain or a substituent, not both. Each substituent needs its own number If two or more identical substituents are bonded to the longest chain, use prefixes to indicate how many: difor two groups, tri- for three groups, tetra- for four groups, and so forth.

Alkanes - Nomenclature 4. Combine substituent names and numbers + parent and suffix. • Precede the name of the parent by the names of the substituents. • Alphabetize the names of the substituents, ignoring all prefixes except iso, as in isopropyl and isobutyl. • Precede the name of each substituent by the number that indicates its location. • Separate numbers by commas and separate numbers from letters by hyphens. The name of an alkane is a single word, with no spaces after hyphens and commas.

Alkanes - Nomenclature Cycloalkanes are named by using similar rules, but the prefix cyclo- immediately precedes the name of the parent. 1. Find the parent cycloalkane.

Alkanes - Nomenclature 2. Name and number the substituents. No number is needed to indicate the location of a single substituent. For rings with more than one substituent, begin numbering at one substituent and proceed around the ring to give the second substituent the lowest number.

Alkanes - Nomenclature With two different substituents, number the ring to assign the lower number to the substituents alphabetically. Note the special case of an alkane composed of both a ring and a long chain. If the number of carbons in the ring is greater than or equal to the number of carbons in the longest chain, the compound is named as a cycloalkane.

Alkanes - Nomenclature